The present invention relates to friction clutches, especially to friction clutches for use in motor vehicles. More particularly, the invention relates to improvements in friction clutches of the type wherein a substantially disc-shaped cover or support can be secured to the crankshaft of the internal combustion engine in a motor vehicle and serves to transmit torque to an axially movable pressure plate, wherein a diaphragm spring is interposed between the support and the pressure plate to bias the latter against the adjacent lining of a clutch disc, and wherein the support is rigidly connected with a counterpressure plate which is adjacent to another lining of the clutch disc. In such friction clutches, the support is connected with and rotates the counterpressure plate through the medium of a distancing device which provides between the support and the counterpressure plate adequate space for the clutch disc and the axially movable pressure plate. The latter normally receives torque from the support by way of several leaf springs.
In many presently known friction clutches of the above outlined character, the counterpressure plate is a casting made of grey iron and having integral projections which constitute the distancing means and are affixed to the support. If the support is a casting made of grey iron or another suitable metallic material, the distancing means can consist of or can include projections which are integral with the support. Irrespective of whether the projections are integral parts of the counterpressure plate or the support, they must exhibit a pronounced bursting strength and, for the reasons of manufacture, their dimensions in the radial direction of the pressure plate and clutch disc are invariably substantial. This contributes to space requirements and bulk of the friction clutch. Alternatively, the rather bulky projections necessitate a reduction of the diameter of the friction linings with attendant reduction of the area of contact between such linings and the two (pressure and counterpressure) plates. For example, if the friction clutch must fit into a given space which is available under the hood of a motor vehicle, and the dimensions of such space in the radial direction of the clutch are rather limited, the outer diameter of each friction lining must be reduced accordingly with attendant reduction of the maximum transmissible torque. Moreover, it is desirable to reduce the diameter of the friction clutch, without unduly reducing the diameters of the friction linings of the clutch disc, on the additional ground that any increase in the diameter of the clutch places the starter for the engine at a greater distance from the transmission, i.e., from the input shaft of the transmission. Such input shaft is driven by the clutch disc and the starter is normally installed at that side of the clutch which faces away from the engine, i.e., rather close to the counterpressure plate. In other words, the provision of a radially compact friction clutch, without unduly reducing the maximum transmissible torque, is of considerable interest to the designer of a motor vehicle, especially of a compact or subcompact vehicle. Moreover, if the starter is to be located at a considerable distance from the common axis of the counterpressure plate, clutch disc and pressure plate, the designer may have to redesign the entire space below the hood in order to provide room for the mounting of the starter at a greater than average distance from the axis of the change-speed transmission.
In accordance with another prior proposal, the counterpressure plate is a practically flat disc-shaped casting, the support is a piece of sheet metal and the distancing means comprises elongated fingers which are integral parts of the support. The fingers are secured to the counterpressure plate by screws which alternate with the fingers, as considered in the circumferential direction of the friction clutch, and are disposed in radially extending spaces between the fingers and the clutch disc. Such constructions do not contribute to an appreciable reduction of the radial dimensions of the friction clutch because the dimensions of the fingers (as considered radially of the counterpressure plate) are rather pronounced. This is due to the fact that the sheet metal of which the support is made is rather thick.
It was also proposed to construct the distancing means as a discrete part which is made of sheet metal, which is secured to the support and which has a recess for a split ring serving to hold the counterpressure plate against axial movement with reference thereto. The means for transmitting torque between the support and the counterpressure plate comprises radially outwardly extending projections which are received in the holes of the distancing part. A drawback of such proposal is that the distancing means contributes significantly to the initial and assembly cost of the clutch. Moreover, the distancing part must be rather thick, as considered in the radial direction of the clutch, in order to provide a groove of adequate depth for reception of the aforementioned split ring which holds the counterpressure plate against axial movement toward or away from the support. This contributes to the bulk, cost and weight of the clutch, especially to the bulk as considered in the radial direction of the counterpressure plate.